Characterization of sperm Ca2+ uptake and its regulation by caltrin I protein

CONRADO AVENDAÑO; ANAHÍ FRANCHI; LAURA C. GIOJALAS; CARLOS E. CORONEL

Carlos Paz-Córdoba, Argentina

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2002

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

The effect of seminal secretory protein caltrin I (calcium transport inhibitor), on extracellular Ca2+ uptake and Ca-dependent acrosomal exocytosis in mouse epididymal sperm has been studied by flow cytometry using fluo-3 to detect cytosolic [Ca2+] changes, and chlortetracycline fluorescence assay to evaluate sperm functional state. Since caltrin I binds to the acrosomal region, the kinetic of both processes was explored. Mouse epididymal sperm loaded with fluo-3 were preincubated for 60 min in Tyrode?s medium for capacitation in the presence or absence of mouse caltrin I. At 15 min intervals, aliquots were removed and the motility, viability, and intracellular [Ca2+] evaluated, while in controls (no fluo-3), the rate of acrosome reacted cells was estimated. In absence of caltrin, the population of sperm incorporating Ca2+ and the fluorescence intensity linearly increased during the 60 min following preincubation, and then remained constant up to next 90 min, while the percentage of reacted sperm increased from 7 to 39 % in the same period. In the presence of caltrin I, cytosolic Ca2+ accumulation and the rate of reacted sperm were dramatically reduced, and around 70 % inhibition was detected in the two parameters along the experiment. Sperm viability and motility were not affected by caltrin. Data suggest that inhibitory activity of caltrin I on sperm Ca2+ uptake prevent premature acrosomal exocytosis to guarantee sperm-zona pellucid primary binding, first step in mammalian fertilization.